Excavators for use in construction or engineering work sites are adapted to perform a variety of works, such as bucket-used ground excavation, building crush and steel rod cutting through the use of a crusher, breakdown of rocks and concrete by use of a breaker, and transportation of scrap steel and rocks by virtue of a grab. The attachments employed in the excavators are changed with another one, depending on the work situations.
Such attachments are releasably mounted onto an arm of excavators so that they can be changed with other type of attachments with ease, if necessary. Referring to FIG. 1, in which a bucket is illustrated as an example of the attachments, it will be seen that the bucket 1 is provided with a pair of spaced-apart, parallel, supporting brackets 3, each of which has coupling holes 3a. An arm 5 and a push link 7 of the excavators are disposed between the pair of supporting brackets 3, and the coupling holes 3a of the supporting brackets 3 are aligned with fastening holes 5a, 7a of the arm 5 and the push link 7, respectively. With such a configuration, the arm 5 and the push link 7 of the excavators are caused to be placed between the pair of supporting brackets 3 and the coupling holes 3a of the supporting brackets 3 are aligned with the fastening holes 5a, 7a of the arm 5 and the push link 7. Moreover, a couple of connecting pins 8 are fitted into the aligned coupling holes 3 and fastening holes 5a, 7a to attach the bucket to the arm and the push link. In this manner, the bucket 1 is releasably mounted to the excavators.
However, the conventional attachment coupling structure requires cumbersome and laborious coupling operations in that an operator should align the fastening holes 5a, 7a of the arm 5 and the push link 7 of the excavators with the coupling holes 3a of the bucket 1 and then fit the connecting pins 8 into the aligned fastening holes 5a, 7a and coupling holes 3a one by one in order to attach the bucket to the arm and the push link. Particularly, an assistant operator should positively take part in checking the alignment state of the fastening holes 5a, 7a with the coupling holes 3a one by one in the alignment process. The transportation and handling of the attachments, the connecting pins and the like is difficult due to their heavyweight nature. And, at the end of coupling operation of the connecting pins, it is necessary to strongly strike the connecting pins by use of a hammer, for instance, thus assuring complete and safe coupling of the attachments. This may lead to waste of time and manpower.
Recently, in view of the above-noted drawbacks, there has been developed and used an attachment coupling device whereby the attachments can be readily connected to the arm of the excavators. As an example, FIG. 2 shows a prior art coupling device disclosed in Korean Laid-Open Utility Model Publication No. 98-63058. The coupling device 10 has a body 12 of which upper portions are formed with a pair of opposite fastening plates 13. Fixing holes 13a are formed at both sides of each of the fastening plates 13 in an aligned relationship with each other. In the meantime, the arm 5 and the push link 7 of the excavator are disposed between the pair of fastening plates 13, and the fixing holes 13a of the fastening plates 13 are aligned with the fastening holes 5a, 7a of the arm 5 and the push link 7 of the excavator. Connecting pins 15 are fixedly fitted into the aligned fixing holes 13a and fastening holes 5a, 7a. In such a way, the attachment coupling device 10 is firmly affixed to the excavator.
Meanwhile, a fixed hook 20 and a movable hook 30 are mounted on each side of the bottom of the body 12 in a spaced-apart opposing relationship with each other. Each of the fixed hooks 20 is formed integrally with the body 12 and has an engagement recess 22 capable of being engaged with a first connecting pin 9a formed at the bucket 1. Further, each of the movable hooks 30 is adapted to rotate about a hinge shaft 30a between a “coupling position” A and a “release position” B, and has an engagement recess 32 capable of being engaged with a second connecting pin 9b formed at the bucket 1. The movable hook 30 is so constructed as to be fixed to the body 12 by means of a fixing pin 34 at the “coupling position” A.
A hydraulic cylinder 40 for causing each of the movable hooks 30 to rotate is mounted to the body 12. The hydraulic cylinder 40 consists of a cylinder housing 42 and a cylinder rod 44. The cylinder housing 42 is affixed to the body 12 through a pivot pin 42a, whereas the cylinder rod 44 is secured to one side portion of the movable hook 30 through a pivot pin 44a. The hydraulic cylinder 40 can be extended or retracted by means of hydraulic fluid to cause the movable hook 30 either to rotate from the “coupling position” A into the “release position” B or from the “release position” B into the “coupling position” A.
The operation of the prior art attachment coupling device constructed as such will be described below. First, under the state that the attachment coupling device 10 is affixed to the arm 5 and the push link 7 of the excavator, the hydraulic cylinder 40 is retracted to cause the movable hook 30 to be placed at the “release position” B. Then, the first connecting pin 9a is caught by the fixed hook 20 so that the first connecting pin 9a of the bucket 1 is engaged with the engagement recess 22 of the fixed hook 20. Thereafter, the attachment coupling device 10 is caused to rotate by the combined action of an arm cylinder 7b and the push link 7 of the excavator so that the engagement recess 32 of the movable hook 30 becomes aligned with the second connecting pin 9b of the bucket 1. Once the engagement recess 32 of the movable hook 30 is aligned with the second connecting pin 9b of the bucket 1, the hydraulic cylinder 40 is caused to extend so that the movable hook 30 is placed at the “coupling position” A. At this time, as the movable hook 30 is placed at the “coupling position” A, the engagement recess 32 of the movable hook 30 will come into engagement with the second connecting pin 9b of the bucket 1. In this state, the bucket 1 is mounted to the arm 5 of the excavator and the movable hook 30 is affixed to the body 12 by using the fixing pin 34 so as to prevent movement of the movable hook 30.
Although the above-referenced attachment coupling device 10 has an advantage in that attachments such as a bucket can be quickly and conveniently connected to or detached from the excavator, one important drawback remains unresolved that an operator himself should affix the movable hook 30 to the body 12 by using the fixing pin 34.
Furthermore, the distance between the first and second connecting pins 9a, 9b of the bucket 1, i.e., pin-to-pin distance, varies depending on the kinds of attachments, and the “coupling position” A of the movable hook 30 may vary accordingly in the prior art device. This poses a problem that the movable hook 30 cannot be affixed to the body 12 by use of the fixing pin 34. If the excavator is driven in this condition, there is a risk that the attachment may be unwantedly detached from the arm of the excavator. A further shortcoming lies in that, as concentrated load is exerted on the hydraulic cylinder 40, the hydraulic cylinder 40 becomes retracted by itself, which results in the attachment being accidentally detached from the arm of the excavator.
In a case where the hydraulic fluid supplied to the hydraulic cylinder 40 leaks out during the course of operation, an accident may arise that the attachment is dropped from the attachment coupling device 10. That is, if the hydraulic fluid supplied to the hydraulic cylinder 40 leaks out, the hydraulic cylinder 40 loses its extension force and the work load exerted on the movable hook 30 is concentrated on the fixing pin 34, which would lead to breakage of the fixing pin 34. Such breakage of the fixing pin 34 will cause the movable hook 30 to move into the “release position” B, as a result of which the attachment 1 becomes disengaged from the fixed hook 20 and thus detached from the excavator.
In addition to the above, the conventional attachment coupling device is disadvantageous in that the radius of rotation of the bucket 1 is too great.
That is, as shown in FIG. 2, mainly because the bucket 1 is designed to rotate about the connecting pin 15 which remains spaced apart from the first connecting pin 9a of the bucket 1, the radius of rotation of the bucket 1 is increased (R1<R2), as compared with FIG. 1 in which the bucket 1 is connected directly to the arm 5 of the excavator. As a result, when the arm 5 of the excavator is retracted, there is a possibility that the bucket 1 may come into collision with a main body of the excavator. The reduced radius of rotation of the bucket 1 may also be a culprit in weakening the excavating force of the bucket.